Human respiratory syncytial virus (RSV) is an enveloped, single-stranded, negative-polarity RNA Pneumovirus of the family Paramyxoviridae. It is a common cause of respiratory tract infections worldwide, including bronchiolitis and other serious illnesses (see, for e.g., Collins and Graham, 2008; Wu et al., 2008). Control and prevention of RSV infection is a global health priority; almost all children are infected with RSV during the first two years of life (see, for e.g., Domachowske and Rosenberg, 1999). In the United States alone, over 2 million RSV-infected infants require medical attention annually (Hall et al., 2009). Infants hospitalized for RSV are also at risk for developing recurrent wheezing and asthma (Escobar et al., 2010).
Polarized, ciliated respiratory epithelial cells are a major target for RSV infection in vivo (see, for e.g., Johnson et al., 2007). RSV infection of ciliated respiratory epithelial cells in vitro occurs on the apical (luminal) aspect (see, for e.g., Zhang et al., 2002). Viral replication in a host cell initiates with attachment of the virus to the plasma membrane via receptor-mediated binding (see, for e.g., Marsh and Helenius, 2006). Candidate RSV receptors have been proposed (see, for e.g., Krusat and Streckert, 1997; Behera et al., 2001; and, Malhotra et al., 2003). Laboratory-adapted strains of RSV show increased efficiency of infection by binding to cell surface glycosaminoglycans (GAGs); however, cells deficient in GAGs are permissive to infection (see, for e.g., Feldman et al., 2000) and the role of GAGs in cellular infection by wild-type, community isolates of RSV is unclear (see, for e.g., Hallak et al., 2007).
Options for treatment are limited, vaccination poses numerous obstacles, and passive prophylactic treatment using anti-RSV antibodies (e.g., palivizumab) is expensive, is not 100% effective, and is limited to those at high risk for severe infection (Wu et al., 2008).
The RSV envelope contains three proteins: small hydrophobic (SH), glycoprotein (G) and fusion (F) (Collins and Graham, 2008). SH protein is not required for virus binding (see, for e.g., Techaarpornkul et al., 2001). RSV G, the heterogeneity of which characterizes RSV subtypes A and B, binds to cell surface glycosaminoglycans (GAGs) at high affinity (see, for e.g., Hallak et al., 2007), but is not an absolute requirement for infection, since mutant RSV deficient in G glycoprotein (RSV ÄG) remains infectious (see, for e.g., Techaarpornkul et al., 2002). Moreover, cells deficient in cell surface GAGs or with chemically modified GAGs are permissive to RSV, albeit at lower levels than cells expressing abundant GAGs (see, for e.g., Techaarpornkul et al., 2002; and Hallak et al., 2000).
Nucleolin is a ubiquitous nucleolar phosphoprotein involved in fundamental aspects of transcription regulation, cell proliferation and growth (see, for e.g., Tuteja et al., 1998; and Chen et al., 2008). Nucleolin has also been described as a shuttling molecule between nucleus, cytosol and the cell surface. Studies have demonstrated that surface nucleolin may serve as a receptor for various extracellular ligands, for instance those implicated in cell proliferation, differentiation, adhesion, mitogenesis and angiogenesis. Nisole et al. (1999), US20040002457A1, and US20020076693A1 disclose that nucleolin is involved in binding of HIV virus to host cells. Nucleolin peptide, nucleotide antibodies, and nucleolin RNAi have all been shown used for inhibiting RSV infection (WO/2011/123945).